1. Field of the Invention
This invention pertains to systems for tuning a variable frequency oscillator and more particularly to systems for accurately tuning a microwave local oscillator to any one of a plurality of selected frequencies using only a single reference frequency source.
2. Prior Art
The local oscillator in a microwave receiver usually includes a crystal controlled oscillator and a frequency multiplier. The crystal oscillator generates a signal at a precisely controlled frequency and the multiplier converts the relatively low frequency signal from the oscillator to a desired microwave frequency. In one type of conventional multichannel receiver, a separate crystal oscillator and multiplier are required for each RF channel, appreciably affecting the receiver's cost and volume. In another type of receiver, a single variable frequency microwave oscillator is tuned to all the local oscillator frequencies; however, additional costly components such as a synthesizer or multiple reference sources are generally necessary to obtain precise frequency control.